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BEST AVAILABLE COP\ Aug. 17 1926.

W. H. PRIESS ELECTRICAL CONDENSER AND METHOD OF MAKING THE SAME Filed June 6, 1921 3 Sheets-Sheet 1 ET 5 t a 0m QN gm @W%Z%d?% w ==========IIIIWIN a a 2%..

BEST AVAILABLE COP.

Aug. 17 1926. A W. H. PRIESS ELECTRICAL CONDENSER AND METHOD OF MAKING THE SAME Filed June 6, 1921 3 Sheets-Sheet 2 BEST AVAILABLE COP Aug. 17 1926. 1,596,374

7 w. H. PRIESS ELECTRICAL CONDENSER AND METHOD OF MAKING THE SAME Filed June a. 1921 3 Sheets-Sheet 5 anveutoz ing.

Patented Aug. 17, 1926.

, UNITED STATES BEST AVAILABLE com rsaaau rATEN'r car es.

WILLIAM H.v PRIESS, OF BELMONT, MASSACHUSETTS, ASSIGNOR TO WIRELESS SPE CIALTY APPARATUS NEW YORK.

COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF ELECTRICAL CONDENSER AND METEonoE MAIiIhTGTEE SAME.

Application name 6, 1921. mutant. 475,216.

This invention relates to electrical condenser-s and methods of making themfThe invention is applicable to condensers of many types, among which are high potential condensers .for use in radio communication, electric power circuits and the like.

Anobject of the invention'is to provide a condenser adapted mechanically and electrically to preserve during service the high pressure initiated upon the condenser stack, (consistingof alternate sheets of foil and dielectric),'during the process of manufacture, and consequent greatest practicable closeness of contact of surfaces of dielectric and conducting sheets, all under conditions of campactness and lightness, the construction being adapted for use not only in service but during the process of manufactur- Another object of the'inv'ention is to provide a compact, eificient condenser. I Another object ofthe invention is to provide a condenser in which the casing functions as a clamp, and'which fmay" belfilled 'With an embedding material, preferably paraflin wax, while maintaining 'intimate contact between the sheets of foil'and dielectric of the condenser stack.

Another object of the invention is to provide in a condenser of the above type means for exerting resilient spring pressure upon the stack, not only during the embedding or filling operation, but also in service.

Another object of the invention is to provide a condenser in which the cooling is a maximum.

Another object of the invention is to provide electrical protecting means between portions of the condenser at high potential difference.

Another object of the in'ventionis toprovide a condenser in which means is provided for allowing expansion of the wax or embedding material while maintaining a high degree of compactness of the embedding material around the high potential termate contact. v

The present invention is an improvement upon the inventions disclosed in my copending applications Serial Number 332,421, filed October 22, 1919; S. N. 370.992, filed April 3, 1920; and S. ,-N. 456,903, filed March30, 1921.

mica.

- The invention consists of thefeatures described hereinafter and illustrated in the accompanying drawings, in. which Figure 1 is'an-elevation, partly in section, taken on the line1-1 of Fig. 2, looking in the direction'of the-arrows; Fig.2is a plan v'iew with the upper plate 2& of-Fig. 1 removed-,6 I 3 v Fig.6 is anj'elevation, partly in section, taken on the line of Fig. 1, looking in t-llfldlIBCtlOIl of thearrows; and

4c is afd'etail perspective view' of a spring pressure plate The p'resent inventionis especially adapted for maintaining the pressure on a stack 1,

consisting of a; number of sections 2 connected'in seri-es at 3 and provided with separators ifinterposed between the sections iandprojectingbeyond the connections for thepurposa of insulating the connections, -which are at-"ajdifierence of potential, from each other; Such a stack 1 consists preferably'of alternate sheets of conductors and :dielectric, preferably of some soft metal foil such as lead and a suitable dielectric such as The stack is constructed and processed substantially as described in my copending'application 456,903 and needs no further description here, the object of such processesb'eing to remove air. moisture and insulating material from between the sheets of foil and dielectric and secure intimate contact between such foil and dielectric The present invention has for its purpose the maintaining of such intimate contact not only during the embedding process, but in service by the means and methods herein described.

As an embodiment of the present invention, I have utilized as a clamping member .a casing 5, preferably of some rigid mate- -rial such as cast iron. or where weight is a factor a strong aluminum alloy. for example. 94% aluminum and 6% copper. This casing, in which the stack is located as illustrated, tapers upwardly and outwardly minal and maintaining the sheets in intiuponits inner surface 6, in order that the distance between the casing and the stack increases from the low potential end of the stack, which is the lower end, to the high tom of the casing, while the upper end of the casing is provided with an inwardlyprojecting ledge 10 having a circular hole 11 therein, such ledge having slots therethrough upon oppositesides to allow free circulation of air around the casing.

In order to maintain in service and during the wax-filling operation the sheets of the stack in intimate contact, I have provided means for maintaining resilient spring pressure upon the stack to allow slight variations in the length thereof, due to temperature changes, in the manner described in 1ny co-pending applications above referred to, although where a cheaper condenseris desired the spring may be omitted. As therein described, so here, this spring pressure means comprises a spring plate 12,- as illustratedin Fig. 4, which is substantially rectangular, has rounded edges and is bowed, when not under stress, as illustrated in Fig. 1. This spring 12 is constructed preferably of some strong springy material such as vanadium steel, and is so designed that it will exert a pressure upon the stack of th order of a ton per square inch of the active surface of the stack when flattened out. In constructing the condenser, if a spring is used, the spring 12 is inserted within the casing 5, with its convex side uppermost and with its ends resting upon the shelves 8 at opposite sides of casing 5. Upon the spring plate 12 is placed a pressure plate 13 of some strong rigid metal upon which the stack 1 rests, the lower section of the stack being elect-rically connected to the casing 1, which constitutes the low potential terminal, by means of a conducting strip 14 (Fig. 1) which is connected to the lower section and clamped between the plates 12 and 13, which in turn are in electrical contact with casing 6, by the clamping of plates 12, 13, to one another and to the inside wall of the bottom of casing 6 by the stack-clamping arrangement now to be described. Mounted upon the opposite end of the stack is a pressure member 15 to which the uppermost section is electrically connected. A terminal stud 16, projecting through hole 11 (Figs. 1 and 3), is threaded into the member 15, this stud constituting the high potential terminal of the stack. Around the stud l6 and resting upon the member 15 is a fish paper washer 17 andmounted around th terminal 16 and upon the washer 17 in the hole 11 (Figs. 1 and 3) is an insulating member 18, provided upon its upper surface witha plurality of concentric ribs or corrugationslS), as illustrated in Fig. 2, whereby the creepage distance between the high potential terminal 16 and the casing is increased: This insulating member 18 may consist of any suitabl insulating material such as lavite, a suitable grade of porcelain, bakelite dilectomor quartz.

After the stack is assembled in the manner above described, a metal clamping collar 20 is placed aroundthe insulating member 18, overla ping the. rim of the same, and is clampec and secured to the top 10 of the casing 1 as a part thereof by 'means of a plurality of screws 21 arranged at thefour corners of the clamping member Fig; 2) and extending through a, gasket 22 (Figs. 1 and 3), to secure water-tightness. The screws 21- are all located equaldistances from-the terminal 16 and each exerts its share of pressure upon the stack, The clamping member 20 is likewise made of some stiff, rigid metal such as cast. iron or the previously-mentioned aluminum alloy. Threaded upon the threaded terminal 16 above insulating member 18 is a. metal sleeve 23. Mounted upon the top of the sleeve 23 and around the terminal 16 is a metal member 24, in the form of .a plate or disk or otherwise secured by nut 25, .and uponthe member 16 above the plate is anut 26, which may beadjusted .to secure a-circuit conductor or lead thereto. After. the condenser has been assembled and clamped together in the manner above described, it may be filled with a suitable embedding material such as oil or parafiin wax through the opening 9, this embedment being indicated at 2-? (Figs. land 3), care being taken to provide upon solidification of the embedment, (as in cases where solid embedmeut of insulating material is used), a space 28 free of wax below the spring plate 12 to allow the expansion of the wax. After the wax has been placedin the casing the closure 29 may be soldered or otherwise secured to close the opening 9, thus completing the condenser.

The metal member 24 has several functions. It not only constitutes a heat dissipating member for the terminal 16, which is the heat-conducting member for the high potentialend of the stack, (since the stack is in good thermo-conductivity with the pressure plate 15. in which terminal 16 1S screwed), but member 245 is also of such an area that it provides a dust cover for the insulator 18, preventing aging and deterioration thereof. Furthermore, the periphery or edge of the high potential member 2% 15 so spaced vertically above the clamping member 20 that it constitutes a protective spark gap therewith, member 20 being connected via casing 5 with the low potential end of the stack 1. Member 2% as thus spaced as shown, closer to metal casing-part 20 than the distance thru insulator 18 from high to low potential conductors, serves to concentrate electrostatic lines across the safetyspark gap and thereby prevent concentration of such lines in said insulator 18 which would be liable to be injuriously effected thereby. Member 24 therefore is a static shield for insulating bushing 18.

The process or method for building condensers of the type herein described is substantially as follows.

After the condenser stack has been treated in the manner described in my application 456,903 above referredto, it is ready to be placed within the casing ,6. The spring plate 12 is first located upon the ledges 8, and upon the spring plate is placed the lower pressure plate'13,or, in case no spring is used, the member 13'may be located directly on ledges 8 (the conducting strip 14 then being clamped directly in contact with the inner wall of the bottom of easing 6) ,and the stack is then positioned 'witliin the casing upon plate 13 with its lower terminal 14 clamped betweenthe, spring plate 12 and pressure n1ember ,f 13. The u'pper'pressure member or terminal plate '15 is then located (as described, by screws 21) on. top of the stack with the threaded rod, stud or terminal 16 projecting above it; the insulator 18 is then secured in position around stud l6 and on top of plate 15; and the whole isclamped preliminarily by means of the clamping member 20.

In the present embodiment of the invention. the condenser is preferably embedded or filled through the bottom through opening 9, the condenser being inverted for this purpose. It will be seen from an inspection of Fig. 3 that there is a direct communication through the opening 9 past the bottom plate members 12 and 13 to points adjacent the top insulator 18 and upper pressure plate 15 to allow complete embedment of stack 1 save at its end faces.

After the parts are assembled as above described, the casing 6 isfilled around the stack to heat the latter and the casing, with hot liquid insulating material such as molten wax, preferably paraflin, and the casing is heated by the application of a Bunsen burner or the like to the outside of the casing '1. The wax is then emptied out of the casing. the casing placed under. an

arbor press'while casing and stack are hot, and pressure applied to the metal member 15 and insulator 18 to compress the stack against thebottom wall of easing 6. The

pressure of the arbor press has reached its optimum value when, from inspection by BEST AVAILABLE COP\ the operator, it is seen that the bottom spring plate 12 is perfectly flat. Under such conditions, the pressure over the opposite ends of the stack is of the order of 2,000 pounds per square inch of the active surface. This pressure not only secures the intimate contact between the sheets of the stack, but the preliminary heating of the stack serves to soften any wax between its sheets, which, upon said subsequent pressure of the arbor press, is squeezed out, bringing the sheets of dielectric and foil in intimate contact. After the arbor press has secured the necessary pressure, and while it maintains such pressure the screws 21 are adjusted in member 15 and easing 6 to maintain this pressure.

The casing is then filled permanently with wax or insulating material through the bottom opening 9, the casing being in verted for this purpose. A false head first is secured around the normally lower end of the casing (opening 9) to provide a head of wax thereabove in the manner described in my application 456,903 above referred to and in patent to Macpherson No. 1,502.34-3 of 22 July 1924. Vacuum is then applied to the condenser casing l and its head, and while under vacuum the casing and head are filled molten wax is poured into the head to fill both casing and head. The casing and head are" then removed from the vacuumtank and the wax is cooled in a gradual manner from the bottom upwardly; that is, the bottom of the molten wax (around insulator 18) is cooled, or heat is applied to the top of the molten wax, or both. The cooling may be by means of an air blast directed against the plate 24' and the surface of the clamp 20 and easing 6 adjacent to it. Hot irons may be kept in the head (around opening 9) to maintain the liquid molten therein. This method of cooling causes the high potential portions of the stack to cool and solidify first (around pressure plate 15 and insulator 18) producing a very solid mass about these points because the solidification occurs there'while under pressure of all the molten wax above. so that as the wax at the high potential locations contracts upon progressive solidification, all otherwise resulting cracks or voids immediately are filled. by gravitation of the molten wax just above, which in turn solidifies, etc; the best effect of solidification being at the lowest part of the molten mass which is at the high potential portions and usually becomes the upper part of the condenser in service. After cooling and solidification of the wax, the head is removed, and the wax cut off flush with the casing and gouged out between the bottom of the casing 1 and spring plate 12 to provide a space 28 free of wax to allow the subsequent expansion of the wax 27,if during service the condenser should heat. This space 28 is in the nature of a safety space to prevent strain upon the casing due to the expansion of the wax and the consequent expansion and loosening of the stack.

The bottom closure 29 over opening 9 is then secured in position, and the condenser is completed. In some cases, the space 28 is omitted, as where oil is used as a filler or embedment. To provide adequately for expansion of any such embedment, the closure 29 may comprise a thin, flexible sheet of metal or diaphragm claimed in my patent 1,4993% capable of expanding or of being distorted by the einbedment in expanding, thus yielding sufiiciently to prevent the 100s cning of the stack sheets through the distortion of the entire casing.

The condenser as above processed and constructed has thefol-lowing advantages. The leakage distance between the terminal 16 and the adjacent portions of the casing on the outside of the condenser (as collarclamp 20) has been increased by the use of ribs or corrugations 19.01. insulator 18. The disc 24,- whieh, is preferably of some. high heat conductive material, asbrass, provides sub stantial heat dissipation fromthehigh 'potential portiom of the stack through.- the pressure plate 15 and stud 16. .The'metho'd 0t filling from-thewbottom claimed in Patent 1,553,5fi9. provides a thorough solid embedm'ent, which is ofuniform consistency 0r holosterie at the h'igher potential portions of. the stack and especially at the high potential portions which are:.at. the bot,- tomof the headgof molten I wax during the bottom-filling step of, the. process, Thewax volume inthe stack- -has been reduced toa :minimum by. thefinjclinedwall, of the casing thereby providing a;maiiinum ofheat conduction frourthe stack-lilo the casing and a minimum volumetric. expan sion of the wax-.throughtemperature rise. Thehe'at convection-and heat, radiating surfaces of the-:condenser .havebeen increased by-member 24 andeby casing-corrugations? more than fifty per cent. over existing designs. Furthermore, the construction of the condenser is.such asto maintaina permanent pressure ofa high orderof magnitude upon the opposite ends of the stack, maintainingthe'sheets of. foil and dielectric in intimate contact andallowing for heat expansion' ofthe stack by, means of the spring 12. The possibility otwa-x cracks occurring in'the condenser.-embedment has been reduced to a minimum, inasmuch as the high potential portions arethe best and most solidly embedded portions. The gouging to remove the-wax to-provide the space 28, and cutting off of the head and surplus wax, as in the present invention, it it doesv produce cracks, produces themat pointswhichare already at the. oasingpotential, and therefore no breakdown from the stack to the casing can occur via any such cracks.

The high potential portions of the condenser are solidly embedded with wax, the wax being particularly solid against the insulator 18, high potential pressure plate 15 and adjacent portions of the casing, thereby not only insuring against breakdown and creepage at these critical locations, but also providing a water-tight seal around the high potential end of the stack through which, moisture cannot pass by pumping action or the like.

The construction above described and disclosed in the drawings provides means whereby the casing not only serves as a clamping member, but also provides means whereby the stack within the casing may be embedded while maintaining the pressure by means of the casing. The space 28 is located at the low potential end of the stack, and in case of expansion of the wax, this expansion is into this space without exerting pressure upon the clamping casing and consequent variation of the pressure of the stack j This invention adapts the entire condenser construction to high duty, both as. to high potentials and high currents, the member 24: aiding materiallyin dissipating heat generated by heavy currents and also serving in theways above described as an electrical protection in respect of high potentials; Also each .and both of these aspects and their efiiciency are materially assisted by the heavy clamping of the stackin combination with the principal novel features of the rest of-the.structure.

' It is to be understood that the invention is. not limited tothe embodiments and features specifically shown and described herein, but that such embodiments and features are subject to changes and modifications without any'departurefrom the spirit of the inventions.

I claim 1..The'combination with a' high duty electrical condenser stack, of a metal casing therefor having its inner wall spaced from the lateral portion of said stack, at least .one end of the stack being held under high mechanical compression against a casing wall, the stack being in electrical and thermal connection via its said end with the metalcasingas a low potential condenser .terminaland a heat dissipator of large surface; said'metal casing having two openings at opposite portions; a terminal extending from a high potential portion of said stack to and thru one of said casing openings; an insulating member closing said opening. and surrounding said high potential terminal; the high potentialportion .of the stack being located near said insulating member; a metalmember located outside the casing, supported by said high potential terminal, electrically and'thermal ly connected thereto, and extending radially therefrom over said insulating member; said metal member having a substantial heat dissipating surface to dissipate heat conducted by the high potential terminal from the stack thru said casing opening; the opposite casing opening being in communication with the interior space between the stack and 'the casing and permitting the introduction of molten insulating material into said space while the condenser is under said compression, to serve thereafter to conduct heat from the sides of the stack to the metal casing as a dissipator; and a closure for said casing opening located opposite said insulating member and attachable after the solidification of said insulating filler.

A high duty electrical condenser of the stack-sheet type, which comprises a stack' of serially-connected sections of interleaved sheets of dielectric and metal foils; an enclosing casing therefor having a metal wall of substantial heat-dissipating surface and with which the foils of a section of said stack are electrically and thermally in high thermal conductivity in good thermal and electrical connection withthe foils of a section of the stack which is substantially remote from said stack-section connected to a metal casing-wall, said terminal projecting to the exterior of the casinggand an H independent metal heat d lpator .of p g ,the exterior atmosphere save those inconstantial dlSSlPZttlIlg surface located outside;

the stack-casing, mounted on and thermally connected with the outwardly projecting 7 portion of said circuit terminal, and extending radially substantial distances from being spaced electrically closer than i, said terminal, from the stack foils connected to said casing, whereby the heat-dissipator is an electrode of a protective spark gap for the stack.

25. A high duty electrical condenser con-- struction comprising a condenser stack and a metal casing therefor with WlllCllsald stack is connected as a low potential terminal, at least one end of said stack be v ing in heat-conducting relation with a wall.

of said casing; said casing being formed with an opening and provided with an 1nsulator closing said opening, said stack be-:

ing provided with a high potential terminal extending thru said insulator to the outside of the metal casing; and a metal member outside the casing and mechanical- 5 1y suggih tg tli 5d? ri i rind thermally connected with said high potential terminal; said metal member extending laterally from said high potential terminal and over said insulator, mechanically protecting the insulator and having a large heat-radiating surface; and said metal member being spaced from the metal casing to constitute a static shield for the insulator and a protective spark gap for the condenser elements.

4:. In an electrical condenser comprising a stack of serially-connected sections of sheets, the combination with a metal casing for said stack and having an outlet opening; an insulating member substantially covering said outlet opening and having a passage for a stack terminal; a stack terminal projecting from one electrical end of the stack through said insulating member; a metal member mounted on the casing and electrically connected with the other electrical end of the stack; and a second metal member mounted on said terminal in thermal and electrical conducting relation therewith extending over said insulating member as a protecting shield therefor, and spaced from said first metal member to constitute an electrode of a spark-gap with said first metal member in shunt to said stack.

5. In an electrical condenser, a casing including insulation; a stack therein comprising serially-connected sections of sheets; a solid metal stud terminal projecting from said stack through said insulation; and a solid metal member supported on and in conducting relation with said stud and beyond said insulation and outside said casing, and spaced from said casing; said metal member having all its surfaces exposed to ducting relation with said stud.

6. In an electrical condenser, a stack of serially-connected sections of sheets; a terminal projecting from one end of the stack;

j, .a casing for said stack having an opening said terminal, said metalheat-dissipator,

through which said terminal projects; an

electrically conducting member supported .on the casing and electrically connected to the other electrical end of the stack; and a solid metal member mounted on said ter- -minal outside the casing and inspaced relationto said. electrically conducting memthermally conducting relation with said stack' and a solid metal member mounted on said terminal outside the casing 1n thermally conducting :relatlon with said termi- 'nal and having all its surfaces exposed to extending out thiii s'aid'cas'ing opening and.

insulating member; a metal member outside the casing, supported by said extend- E312 terminal, electrically and thermally connected therewith, and extending laterally tl'iercfrom and over said insulating member; said inetal member having large heat-dissipatii'ig surfaces and being spaced from said metal casing to constitute a protective spark gap bctween iliefopposite potential terminals of the condenser; said condenser elements of l'iiglier pdtential andthe portions of the casing adjacent thereto-being spaced from one another; and an insulating heat conveying. medium in the space between the 'lieatdi'ssipator.

"condenserelenientsandthe metal'casing as a 9. I l i'e' icdrnbinzititir'ifivith a :high duty electrical condenser stack, of "a metal casing f'theiefor havin its 'inner'wal'l'spaced from the lateral portion of fthe:'stacl at least one end or the stack being eld under high omechanical 1coiripress'ibiiagarms'ta wall of the and thermally honn'ected via its said-end with" tphefiiigata1 casing "as "ii-low potential condenser terminal and a heat T dissipator of large garage; said casing-having" an opening and a terminal extending from a high potentialportiono'f said stack toand fth'ru said casing'fiopening; 'an' insulating frriembe r closing the's a'id opening and surnding potential terminal and em] member outside theca'sijng, supbysaid high potential terminal, electawn -and thermally connected therewith,

and extending 'lat erally 'therefrom' and over said insulating member; said metal member "having a substantial heat-dissipatin g surface to dissipate heat conducted 'by'the high potential terminal from the stack thru the casing openihg, a'nd' being spaced electrically' closer than said high potential terminal, from'the'end of the stack which is connected to .the casing, wherebysaid dissipating member constitutes -also an electrode of a protective spark gap for the stack and a staticshieldifor said insulating member.

10. In an electrical condenser, a metal casing provided with heat-radiating ribs externally; a stack oiflserially-connected sections of'sh'eets 1ns1de sa d casing; 'means for clamping the stack from end toend Wltllll'l' the casing; an insulating top cover plate for the casing; a terminal lead projecting through said insulating cover plate to the outside of the casing; and a metal member secured to said terminal lea-d outside the casing, and extending over, near to but separated from said insulating top cover plate to protect the same, said metal member being arranged in conductive relation with said terminal lead to co-operate with said casing ribs in conveying heat from the internal stack to the external atmosphere.

11. The combination with a high duty electrical condenser, of a metal casing therefor having its inner wall spaced therefrom, and having two openings at opposite portions thereof; a terminal extending from a high potential portion of said condenser to and thru one of said casing openings; an insulating member closing said opening and surrounding said high potential terminal; the high potential portions of the stack being located near said insulating member, and a low potential end of the stack being in heat-conducting and electrically conducting relation with a wall of the metal casing as a heat dissi'pa-tor and condenser terminalg'a "metal member located outside the casing, supported by said high potential terminal, electrically and thermally connected thereto, and extending laterally therefrom and over 'said insulating 'nd'ember; said metal member having a substantial heat dissipating surface 'to dissipate heat conducted by the high potential terminal from the stack thru the casing opening; the opposite casing opening heling'in communication with the interior space between the stack and the casing and permitting the-introductionof molteninsulating material into said-space while the condenser is under said compression, to serve there after to conduct heat from the sides of the "stack'to'the metal casing-as a dissipator; and -a closure for said casing opening opposite saidinsulating member and attachable after solidification 0t said insulating filler. 12. In an electrical condenser, a metal casing having ribs thereon for increasing the heat-radiation and conduction, a spring plate, and a pressure plate mounted in said casing at one end, a condenser stackcomprising sections connected in series resting upon said plates and having its adjacent end electrically'connected to said plates and the casing,-the casing constituting a terminal there- 'for, said casing tapering upwardly and outwardly from one end ofthe stack towards the high potential end of the stack, a pressure member resting upon the high potential end of the stack and having a threaded stud projecting vertically therefrom, an insulating member surrounding said stud, above said high potential pressure plate and having a plurality of concentric ribs ther'eonfor increasing the creepage distance, a .metal clamping collar overlapping said insulating member, screws arranged around said collar and threaded into the casing for clamping the insulating member against said high potential pressure member, a metal disc secured in conductive relation to said stud and spaced from said collar providing a spark gap therewith, and an embedment of solid holosteric insulating material packed around the high potential end of the stack, a space being provided between the lower end of the casing and the spring plate to allow expansion of the insulating material, the bottom of the casing having an opening adjaeent said space through which the casing may be filled with the insulating material, and means for closing said openin 13. In an electrical condenser, a metal casing, condenser elements within said casing and electrically connected thereto, an insulating bushing mounted on said casing, a

high potential terminal connected to said elements and extending through said bushing, and means for preventing electrical losses in said bushing and mounted above the same on said terminal, said means also constituting an electrode of a protective spark gap.

'14. A high potential electrical condenser comprising condenser elements and a metal casing therefor to which said elements are connected as a low potential terminal; said casing being formed with an opening and provided with an insulator closing said opening; said condenser elements being provided with a high potential terminal extending outside the condenser'casing thru the insulator; and a metal member located outside the casing and mechanically supported by and electrically connected with said high potential terminal; said external metal member extending laterally from said high potential terminal and over said insulator and closer (in a line outside said insulator) to the nearest portion of the metal casing than the shortest distance via the insulator between the high and low potential terminals of the condenser, whereby said metal member serves as a static shield for said insulator and as an electrode of a protective spark gap for the stack.

15. A high duty electrical condenser of the stack-sheet type, which comprises a stack of serially-connected sections of inter leaved sheets of dielectric and metatfoils; an enclosing casing therefor having a metal wall of substantial heat-dissipating surface and with which the foils of a section of said stack are electrically and thermally in good connection; the sides of said stack being spaced from the enclosing casing; each section of said stack comprising sheets of mica and metal foils, adjacent sections being insulated from one another at their faces but electrically and thermally connected together in series via portions of said BEST AVAILABLE COP: 7

foils projecting from the stack into said space around the stack-sides; a circuit terminal in good thermal and electrical connection with the foils of a section of said stack which is substantially remote from said stack-section which is connected to the metal casing-wall, said terminal projecting to the exterior of the stack-casing; a heatconducting insulating filler in said space and surrounding said terminal and conducting heat from the stack foils to said metal casing-wall and to said circuit terminal; and an independent metal heat dissipator of substantial radiating surface and located outside the stack-casing, mounted on and thermally and electrically connnected with the outwardly projecting portion of said circuit terminal and extending radially substantial distances from said terminal, said radially extending portion being spaced electrically closer to the metal casing than the shortest distance thru the insulating filler between the casing and the terminal.

16. A metal-encased stack condenser wherein the casing has an opening for a lead from one stack terminal and itself is electrically and thermally connected to another stack terminal of different potential; a casing-cover of insulating material over said opening and around said lead; safety means electrostatically protecting said stack and the insulating material of said cover, said means comprising a metal member located outside the metal casing, supported by and thermally and electrically connected to said terminal lead and extending radially and annularly therefrom over said casing opening and insulating cover, and spaced from the metal of the casing around the opening therein to constitute it an electrode, of a safety spark gap for said stack and a static shield for the insulating material of said cover.

17. A metal-encased stack condenser wherein the casing has an opening for a lead from one stack terminal and itself is electrically and thermally connected to another staek terminal of different potential; a cover of insulating material over the casing opening and secured to the" casing around the opening and projecting outwardly of the opening; and an annular metal projecting shield connected to said lead and located outside the casing beyond the insulating cover but spaced from the metal of the casing so as to be an electrode of a safety spark gap in shunt to the stack and a static shield for the insulating mate rial of the cover, said shield serving also to protect said cover mechanically and also having a large surface dissipating heat conducted from the stack by said terminal lead.

18. A metal-encased stack condenser wherein the casing has an opening for the extension of a lead from one stack terminal and itself is connected to another stack terminal of opposite potential and wherein an insulating member covers said opening; a rigid construction including a stack terminal lead structure clamped with the stack inside the casing and projecting thru the casing opening and cover; and an annular metal static shield for the insulating cover, said shield being supported on said terminal lead outside the casing and extending in proximity to the metal of the casing to constitute it an electrode of a safety spark gap shunting the stack.

An electrical condenser comprising a stack of serially connected sections, a metal enclosing casing therefor comprising a cover of insulating material thru which a high potential terminal of the stack projects said k rejecting terminal carrying a conducting member extending radially in substantially all directions from said terminal and having its periphery spaced from the metal of the casing constituting it an electrode of a protective spark gap for the stack, said conducting member also constituting a static shield for the insulating material of the cover.

20. A metal-encased electrical stack condenser wherein the casing has an opening for the extension of a lead from one terminal of the stack and itself is connected to another terminal of the stack of different potential, and a radially extending annular projection over the casing'opening; of that portion of the terminal lead which is located outside the casing,- said projection" having a large heat dissipating surface and being spaced from the of the enclosing opening to constitute it"anelectrode of a protecting spark gap often-i011 the other electrode is said casing.

21. An electrical condenser comprising a stack of serially connected sections, a metal enclosing casing therefor comprising a cover of insulating material thru which a high potential terminal of the stack projects, said stack and easing being spaced from one another to receive a fusible insulating filler; and said high potential terminal carrying a conducting member thermally connected thereto and extending radially in substantially all directions therefrom thereby constituting a static shield for said insulating cover, the large heat dissipating surface of said shield serving to facilitate solidification of the insulating filler adjacent the high potential parts of the condenser with which said shield is in thermal communication via the high potential terminal.

22. A metal encased stackcondsenser wherein the casing has an opening for a lead from one terminal of the stack and itselfis electrically and thermallyconnected to another stack terminal of different potential; a cover of insulating material for said casing'opening, the metal of the casing extending around the insulating cover and assisting in supporting the cover in place, and the insulating cover projecting outside the casing and perforated to permit projection of said terminal lead; and a safety spark gap electrode and static shield consisting of an annular extending member of conducting material mounted on the proj'ecting portion of said terminal lead outside the casing and beyond the outwardly projecting insulating cover and extending radially from the projecting terminal into protecting'spark gap proximity to the metal of the casingaround the casingopening and insulating cover.

lVILLIA-M H. PRIESS. 

